Electric induction-furnace.



No. 861,031'. PATENTED JULY 2s, 1907.

J.HRDEN.

ELECTRIC INDUCTION FURNACE.

APPLICATION FILED JAN.24, 1907.

- UNITED STATES PATENT OFFICE.

lJOHANNES H RDN, OF LONDON, ENGLAND, ASSIGNOR TO THE GRNDAL KJELLlN.

' COMPANY, LIMITED, OF LONDON, ENGLAND.

ELECTRIC INDUCTION-FURNACE.

Specification of Letters Patent.

Patented July 23, 1907.

Application led January 24:, 1907. Serial No. 353,842.

To all whom 'it may concern:

Be it known that JOHANNES HRDN, 'a subject of the King of Sweden, residing at 2O Abchurch Lane, in the city and county of London, England, engineer, has invented certain new and useful Improvements in or Relating to Electric Induction-Furnaces, of which the following is a specification.

This invention relates to' electric induction furnaces, such as those of the Kjellin type, which are constructed upon thel principle of a transformer, of which the charge to be melted or otherwise treated forms the secondary. Hitherto these furnaces have been operated successfully with single phase alternating current only. y

Various attempts have been made to utilize polyphase alternating currents such as two or three phase currents, one annular bath or fusion chamber being provided for eachphase, either separate or in conjunction. But as the losses caused by heat radiation were found very high, in fact, about nine kilowatts per square foot of the bath surface, these attempts were'not successful, and it was found necessary to convert the polyphase current into single-phase by means of special motor generators, lthus greatly increasing the original cost of the installation. Moreover, as the fusion chambers or seeondaries have to be placed at a considerable distance from the primary coil, an arrangement of two or three fusion chambers will greatly increase the magnetic leakage in the transformer, thus causing a low power factor and inefficient operation of the generating plant.

The chief object of the present invention is to overcome the above mentioned difficulties and defects in applying polyphase alternating currents for the operation of electricinduction furnaces.

According to this invention polyphase alternating currents are employed in the working of electric induction furnaces by directly or indirectly combining therewith one or more transformers to convert the polyphase currents of the supply mains into single-phase currents in the induction furnace. For this purpose the primary windings of the transformer comprising the induction furnace are connected to the secondary windings of one or more transformers whose primary windings are connected to the different phase windings of a polyphase system, the connections being such that the currents induced in the aforesaid secondary windings are all in the same direction, but possess phase differences corresponding or proportionate to the phases of the polyphase system.

In order that the said invention may oe clearly understood and readily carried into effect, the same will now be described more fully with reference to the accompanying drawings in which?- Figure .1 is a diagram of an induction furnace having two transformers independently connected to a two' phase system. Fig. 2 is a similar diagram in which the two transformers are combined. Fig. 3 is a diagram showing the transformers combined with the induction furnace. Fig. 4 is a diagram illustrating the application of this invention to a three-phase system.

A is the annular fusion' chamber surrounding the middle member B of the -induction furnace, the side members of which are indicated by the letters B1, B2.

Referring to Fig. l, C, D represent the cores of two transformers whose primary windings C1 Dl are connected to the mains C2 D2 l'eading from the phase windings of a two-phase system. .The secondary windings B3 B4 of these transformers are .wound co-axially upon the primary windings O1 Dl and are so connected in series that the current inone is flowing in the same direction as the current in the other. Hence the total pressure obtained across the two secondary windings B3 B4 will be equal to one divided by the square root of two times the sum of the pressures due to the windings B3 and B4 separately. These secondary windings are connected to the primary windings B5 of the single-phase induction furnace which may be of usual construction. Tests have shown that the power factor obtained by this arrangement is quite normal.

In Fig. 2, the two transformers C D are shown cornbined, an advantage of this construction arising from the fact that the weight of iron required is less than when they are separate, since the sectional arca of the middle member CX need only be equal to one divided by the square root of two 5 2.) times thesum of the operation andresults obtained are similar toy those obtained from the arrangement shown in Fig. l.

In Fig. 3, the transformers are combined with the induction furnace itself, the primary windings C1 D, and also the secondary windings B3 B being wound upon the outer members B1 B2 of the induction furnace. In this case, the windings B3 B4, which are secondary windings with respect to the windings C1 D, are the primary windings with respect to the Charge contained in the annular chamber or bath A.

The advantage of the construction shown in Fig. 3 is a great economy of material occasioned by employing the furnace core B as the middle member of the transformer, while as well serving as means forpositioning thc magnetic flux.

In order to decrease the leakage field caused by the current induced in the annular chamber or bath A, additional windings BX may, if desired, be placed around the middle member B of the induction furnace.

These additional windings, if used, as well as the sectional larea of the member B, should bear approximately the same relation to the windings B3 B4 and the outer members Bl B2 respectively as that set forth with reference to the middle member of the construction shown-in Fig. 2, An advantage of this construction is its compactness and saving of labor in manufacture.

Fig. 4 illustrates diagrannnatically a method oi converting a three-phase system into a single-phase system or use with an induction furnace. The upper part oi the diagram represents the well known Scotts method oi phase transformation tor converting a three phase to a two-phase system. E, F and Gr are windings connected to a system of three phase supply mains and B3 B4 are two sccondaries, the arrangement being such that the times-phase system is converted into a two phase system as will be readily understood. The secondary windings B3BA1 are then connected to or combined with the primary windings B5 of the induction furnace with similar results to those described with reference to the Figs. l, 2 and 3.

Although two and three-phase systems have been considered in the above description, it is not desired to limit this invention to these systems only, but to apply it to polyphase systems generally and in conjunction with any known method of phase transformation.

What I claim and desire to secure by Letters Patent oi the United States is 1. ',lhe combination with an electric induction furnace and a source of polypliase alternating current, of a plurality of primary windings electrically connected to and corresponding in number with the different phase windings of the aforesaid source, a plurality of secondary windings corresponding in number with the said primary windings, and magnetic cores carrying said primary and secondary windings and forming part of the core of the induction furnace, substantially as and for the purpose specified.

2. The combination with an electric induction furnace and a source of polyphase alternating current, of a plurality of primary windings electrically connected to and correspondingin number with the different phase windings of the aforesaid source, a plurality of secondary windings corresponding in number with the said primary windings and electrically connected so that the currents induced therein serve as the primary current of the induction furnace, and magnetic cores carrying said primary and secondary windings and forming part of the core of the induction furnace.

3. The combination with an electric induction furnace and a source of polyphase alternating current, of a pluralit'y of primary windings electrically connected to and corresponding ln number with the different phase windings ofthe aforesaid source, a plurality of secondary windings corresponding in number with the said primary windings, a primary winding on the central magnetic core of the induction furnace and electrically connected with the aforesaid secondary windings, and outer magnetic cores carrying said primary and secondary windings and forniing with the central core carrying the primary windlng, the transformer structure.

4. The combination with an electric induction furnace and a source of polyphase alternating current, of a plurality of primary windings electrically connected to and corresponding in number with the different phase windings of the aforesaid source, a plurality of secondary wind ings corresponding in number with the said primary windings and wound coaxially therewith, a primary winding on the central magnetic core` of the induction furnace and electrically connected in series with the aforesaid secondary windings, and outer magnetic cores carrying said primary and secondary windings and forming with the central core carrying theprimary winding, the transformer structure.

5, The combination with an electric induction furnace and :1 source of polyphase alternating current, of a plurality of primary windings electrically connected to and corresponding in number with the diiferent phase windings of the aforesaid source, a plurality of secondary windings corresponding in number with the said primary windings, and electrically connected so that the currents in duced therein serve as the primary current of the induction furnace, and outer magnetic cores carrying said primary and secondary windings and forming with the cenA trai magnetic core of lthe induction furnace, the transformer structure.

' 6. The combination with an electric induction furnace and a source of polyphase alternating current, of a plurality of primary windings electrically connected to and corresponding in number with the different phase windings of the aforesaid source, a plurality of secondary windings corresponding in number with the said primary windings, a primary windingl on the central magnetic core of the induction furnace and electrically connected in series with the aforesaid secondary windings, and outer magnetic cores carrying said primary and secondary windings and forming with the central magnetic core of the induction furnace, the transformer structure.

ln testimony whereof I afiix my signature in presence of two witnesses.

JOHANNES HnDnN.

Witnesses:

Trios. J. WALKER, CHAs. J. H. YnLvnn'roN. 

